This is a good question. There is no one place where a hierarchy is given. However, if we piece things together we can come to a few educated conclusions.
First, Atticus and his family are pretty high up on the social hierarchy. Scout on several occasions talks about their family's heritage in Maycomb. Also Atticus is a lawyer and Jack, his brother, is a doctor. Also Alexandra is akin to a socialite.
Second, there are others in the town like Heck Tate and Ms. Maudie. They are the average citizens of the town. They are white and solidly middle class.
Third, you also have poorer citizens, like the Cunninghams. We know that they are poor because Walter did not have food or money for food at school. Scout says that they just get by. Also Walter's father does not pay Atticus for his legal services in money but in nuts and other food stuff.
Below the Cunninghams you have the really poor - Bob Ewell and his family. The town lets them do whatever they want, like hunt off season, because they feel sorry for him.
Finally, you have the blacks. They are generally taken advantage of. This is why Tom was accused of a crime, even though he was innocent.